Our climate is changing: it is getting warmer. The average annual temperature in the Netherlands has risen from around 8.5 oC since 1900 to almost 12 oC in 2023. During that period, 2023 was the warmest year ever with a heat wave of ten days in July (temperature higher than 25 o C ), of which five were tropical days (temperature higher than 30 oC ).

Het wordt steeds warmer

It is getting warmer (from: KNMI – The State of our Climate, 2023).

In the cities it gets even warmer, often many degrees up to 80 oC higher, also in Delft. All the stone and concrete retain a lot of heat.

In de steden is het veel warmer dan op het platteland

It is much warmer in cities than in the countryside (from Rijkswaterstaat & RIVM, Atlas Leefomgeving).

Such high temperatures are very unpleasant. Can even be dangerous. So we all look for cooling. And what is better than water? We play with water, dive into the pool or the sea.

Waterreservoirs

Water cools, also in the Van Leeuwenhoek Park.

Or we sit under a tree. Its shade protects us from the sun. But trees also evaporate water. And evaporation also cools. That’s why you get cold when you get out of the pool.

Fortunately, 2023 was also the wettest year in the period 1900 – 2023. So there was enough water to cool you down. At least, that’s what we thought. On average, 1153 mm of rain fell in the Netherlands, in Delft even 1300 mm. That is normally 851 mm. Our climate is changing: it is not only getting warmer, but also increasingly wetter. However, that rain is not evenly distributed across the Netherlands. Delft is one of the wettest places.

Elsewhere we read how Delft processes all that water. In the past, people counted on precipitation peaks of 20 mm/hour. Nowadays, we already count on peaks of up to 58 mm/hour and very wet days with 50 – 200 mm of precipitation. These occur about 1% of the time. During normal wet days, about 10 – 50 mm of precipitation falls, about 9% of the time.

Het wordt steeds natter en Delft is erg nat

It is getting wetter and wetter, and Delft is very wet (from: KNMI Annual Review 2021, The Climate Story of 2021).

Oddly enough, 2023 was also very dry. This is due to more than four weeks of drought in May and June, with lots of sun. This is precisely the growing season for many plants and trees. But February and September were also very dry. This is why there was a large precipitation deficit in the summer. This means that there is too little rainfall to keep nature healthy and the groundwater at the right level.

This trend continues: we are getting warmer and wetter years, more tropical days and longer periods of drought. What problems does this cause? We can read about it here. And how is Delft preparing for these climate changes? This is stated in these Policy Rules that the municipality has drawn up.

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